1. Field of the Invention
The present invention relates generally to a compressor, and more particularly to a reciprocating type compressor having an inter cooler.
2. Description of the Prior Art
Operational gases which are compressed by a compressor, such as a reciprocating piston type of compressor, are typically heated as a result of the work applied thereto during the compression process. Heating of the gas is disadvantageous, because it reduces the density of the gas, thus reducing the amount of work output (i.e., compressor performance is adversely affected). Also, the heating of the gas can adversely affect the performance and endurance of seal members which may be contacted by the gas.
A conventional reciprocating type compressor is disclosed, for example, in Japanese Patent laid open Publication No. 59-185883 published on Oct. 22, 1984. This conventional reciprocating compressor includes an inter cooler interposed between a cylinder and a cylinder head. A compression space is defined between the cylinder head and a reciprocable piston disposed in a bore of the cylinder. The inter cooler defines a refrigerant passage through which a refrigerant is conducted. A gas inlet for operational gas is provided, the inlet communicating with an inlet valve which, in turn, communicates with the compression space to conduct operational gas into the compression space in response to an intake stroke of the piston. A gas outlet is provided for discharging operational gas during a discharge stroke of the piston. That gas outlet communicates with an outlet valve which, in turn, communicates with the compression space.
In one embodiment, the refrigerant passage overlies at least a substantial portion of the cross section of the cylinder bore, and a plurality of narrow, i.e., small-diameter conduits extend through that passage in heat-exchange relationship therewith. A first group of those conduits communicates the inlet valve with the compression space, and the group of remaining conduits communicates the compression space with the outlet valve. During the piston intake stroke, incoming gas passes through the first group of conduits and is cooled; during the piston exhaust stroke the discharging gas passes through the second group of conduits and is cooled. The cooling of the gas tends to offset any heating of the gas occurring as a result of the work applied thereto during the compression process, thereby alleviating the above-discussed disadvantages associated with such heating.
However, since both the inlet and outlet valves communicate with the compression space via narrow conduits, a drawback occurs. That is, during a discharge stroke of the piston, some of the operational gases will be forced into those of the narrow conduits which communicate with the inlet valve and thus will not be discharged. The volumes of those narrow conduits thus constitute dead air spaces which reduce compressor efficiency. Also, during a piston intake stroke, a large pressure loss results from the fact that the incoming gases are restricted to pass through the narrow conduits.
Further, in the above-described conventional reciprocating type compressor, since the cross-sectional area of the refrigerant passage taken in a direction perpendicular to the narrow conduits of the inter cooler is relatively large, the flow speed of the refrigerant is relatively low. Therefore, there occurs a drawback in that the rate of the cooling of the operational gas by the inter cooler is also relatively low. While such cross-sectional area can be reduced by increasing the number or the diameter of the conduits for the operational gas, the flow speed of the operational gas becomes reduced as a consequence and the rate of cooling of the operational gas by the inter cooler remains low.
In another embodiment of the above-referenced publication, the refrigerant passage overlies only a portion (e.g., about one-half) of the compression space, the remainder thereof being overlain by the inlet valve. Thus, only the outlet valve communicates with the compression space via the narrow conduits. While such an embodiment alleviates the above-discussed drawback relating to dead air space, it would not alleviate the drawback relating to a low cooling rate. In fact, since the volume of the refrigerant passage is decreased (as compared with the first embodiment), the overall cooling rate would be further reduced.